The invention relates to a reciprocating compressor in which a piston reciprocates within a cylinder bore and specifically relates to a technique for lubricating the sliding surface between the cylinder bore and the piston.
In reciprocating compressors, an oil separator is provided on the downstream side of a discharge chamber, and after a refrigerant gas is separated from a lubricating oil by the oil separator, the lubricating oil is directed to and lubricates a sliding surface between a piston and a cylinder bore due to the pressure differential between the suction and discharge sides and is then returned to a drive chamber on the low-pressure side.
In order to improve the effect of lubricating the sliding surface between the piston and cylinder bore, the compressor has an oil groove extending axially toward the outer circumference of the piston. In a known configuration, the lubricating oil is supplied from an oil hole and is guided to the sliding surface via the oil groove, which actively communicates with the drive chamber. This lubricating technique is disclosed, for example, in Japanese Laid-open Patent Publication No. 10-141227.
However, in systems in which the lubricating oil is separated from the refrigerant gas at the sliding surface between the piston and the cylinder bore due to the pressure differential between the suction and discharge sides, the use of a configuration comprising the oil groove on the outer circumference of the piston creates the problems of leakage of the refrigerant into the drive chamber via the oil groove and a decrease in performance due to the active communication of the oil groove with the drive chamber. This phenomenon is particularly problematic in compressors that employ carbon dioxide (CO2) as a refrigerant due to the large pressure differential between the suction and discharge pressures.
The invention has been designed with due consideration given to these conventional problems and has objectives to facilitate an adequate lubricating effect for the sliding surface between the piston and the cylinder bore of a reciprocating compressor and to prevent leakage of the refrigerant.
In order to attain the above objectives according to the invention, an oil sump is provided on the sliding surface between the piston and the cylinder bore in a reciprocating compressor. As a result, the lubricating oil collects in the oil sump, the lubricating oil ensures an adequate lubricating effect for the sliding surface, and seizure is prevented. Moreover, a configuration is taught in which the oil sump does not communicate with the drive chamber, which is situated on the low-pressure side, so that connection essentially occurs only via the gap between the piston and the cylinder bore. This enables the amount of refrigerant that leaks toward the drive chamber side to be reduced and prevents a drop in performance.
Consequently, lubricating oil directed toward the oil sump is preferably a lubricating oil separated from the refrigerant for discharge, and a configuration in which the lubricating oil is directed due to the pressure differential between the suction and discharge sides is preferable. This construction is particularly effective to reduce the amount of leaking refrigerant when utilized with a compressor that uses carbon dioxide as the refrigerant.
It is also preferable to locate the oil sump around the entire circumference of the sliding surface. In this case, the entire circumference of the sliding surface is sealed and the lubricating oil collects in the oil sump, which further reduces the amount of refrigerant that leaks toward the drive chamber.
It is also preferable to dispose the oil sump on the outer circumference of the piston. For this configuration, the intermediate axial portion of the outer circumference of the piston preferably has a small diameter. By disposing the oil sump on the piston, the oil sump can be manufactured using the most commonly known outer circumference processing methods in machine tooling and as a result, the associated processing is easily performed.